XALITZINTLA, Mexico — The white-capped volcano that looms over Mexico City emitted a terrifying low-pitched roar Friday and spewed roiling towers of ash and steam as it vented the pressure built up by a massive chamber of magma beneath its slopes. Authorities prepared evacuation routes, ambulances and shelters in the event of a bigger explosion.
Even a large eruption of the 17,886-foot cone of Popocatepetl is unlikely to do more than dump ash on one of the world's largest metropolitan areas. But the grit could play havoc with Mexico City's busy airport, and tens of thousands of people in the farming villages on its flanks could be forced to flee.
Popo, as it's commonly known, has put out small eruptions of ash almost daily since a round of eruptive activity began in 1994. A week ago, the eruptions started growing larger and authorities slightly elevated the alert level for people living nearby.
Before dawn on Friday, the mountain moved into what appeared to be a new level of activity, spitting out dozens of ash clouds and shot fragments of glowing rock down its slopes while frightening the residents of surrounding villages with deep roaring not heard in a decade.
People in the village of Xalitzintla said they were awakened by a window-rattling series of eruptions. Mexico's National Disaster Prevention Center said one string of eruptions ended in the early morning, then the volcano started up again at 5:05 a.m., with at least 12 eruptions in two hours.
"Up on the mountain, it feels incredible," said Aaron Sanchez Ocelotl, 45, who was in his turf grass fields when the eruptions happened. "It sounds like the roaring of the sea."
A 35 million cubic foot chamber of magma is seething about six miles beneath Popocatepetl, Roberto Quaas, director of the disaster prevention center, said at a news conference laying out emergency preparations.